The invention relates to a method of dispensing foam and to an apparatus according to the preamble of claim 1 and claim 4, respectively.
Foam dispensers of that kind are frequently used in washrooms and toilets, especially of public facilities, restaurants, etc. They are also found in areas having high hygiene requirements, such as the food industry, healthcare etc., where they are often operated with soap solutions that contain disinfectants.
WO 90/14037, FIG. 4, discloses a concentrically constructed foam dispenser that sucks in air from the dispenser housing via a non-return valve, compresses it and, at the same, feeds soap solution out of an intermediate vessel. The two media are combined in a mixing chamber; the coarse-bubbled foam formed therein is subsequently homogenised by means of a foamer and expelled for hand washing.
The known apparatus is relatively bulky and consists of numerous individual parts which in time become soiled and clog and/or contaminate the dispenser. In addition, it has a tendency to drip since, in the mixing chamber and in the dispenser, the residual foam collapses to some extent and, especially during prolonged breaks in operation, agglutinates to some extent.
The object of the invention is therefore to provide a method for controlled foam production and delivery and to construct a foam dispenser that does not have the disadvantages of the prior art and, in particular, does not have a tendency to drip.
The dispenser to be provided is to be reliable in operation and provide improved hygiene conditions. It is intended to have a large intermediate vessel with an easily visible filling level indicator so that sufficient time is available in every case to replace the empty supply bottle with a new, filled supply bottle. In addition, the dispenser is to be economic to manufacture and is to require a minimum of maintenance.
According to the invention, the object is achieved by the features of claim 1.
According to the method, in the first phase, after the formation and dispensing of the foam, the dispensing nozzle is blown clear; in the second phase, a slight negative pressure is produced there, which destroys the remaining foam.
The liquid lamellae forming the foam undergo expansion as a result of the back-suction (negative pressure) and, owing to their thermodynamic instability, are broken up at the inner surface of a nozzle/expansion body, that is to say, a minimum amount of soap solution is produced there which, with the next positive stroke of the piston, is foamed again and expelled (with the foam portion).
As a result of that measure, the nozzle space always remains clean; it does not become encrusted and therefore the dispenser is capable of operating even after long breaks in operation.
Developments of the subject-matter of the invention are characterised in dependent claims.
The method according to claim 2 can be integrated very easily into existing constructions of air cylinders.
The development according to claim 3 is a solution that is especially interesting from an economic viewpoint.
Residual foam present in the foam delivery bore is successfully destroyed by an expansion upstream, with the result that no dripping occurs.
The apparatus according to claim 5 has the advantage of a very hygienic and operationally reliable construction.
Passing over a single air passage, which is mentioned in claim 6, is especially efficient and replaces the valves, air directing means, air guides, stepped piston rods for temporary air supply etc. which are required in other conceivable constructions.
The embodiment according to claim 7 is especially effective.
The construction according to claim 8 prevents the ingress of germs etc. into the dispenser and ensures a decisive improvement in hygiene conditions.
The embodiment according to claim 9 serves to prevent the supply vessels from being confused with one another; it increases operating reliability and serves to ensure that suitable soap solutions are used, especially in critical areas (food production and distribution, healthcare etc.).